Press product forming method

ABSTRACT

Provided is a press product forming method for press-forming a curved press product. The curved press product is formed into a hat-like cross-section including an upper surface portion, side wall portions, and flange portions. The press product forming method includes: a pre-forming step of forming, at a widthwise end portion of a flat plate-like blank, at least one bending portion extending along a longitudinal direction; and a main forming step of forming the upper surface portion and the side wall portions under a state in which the bending portion is left.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Japanese Patent Application No. 2012-035781 filed on Feb. 22, 2012, the entirety of which is hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This disclosure relates to a press product forming method.

2. Description of the Related Art

There is known a technology of press-forming a press product, with Japanese Patent Application Laid-open No. 2010-36217 disclosing one example.

However, in a case where the press product is a curved press product which exhibits a curved shape in plan view or in side view, an excess material resulting from the curved shape is more likely to cause forming defects, such as wrinkles, in the flange portions.

FIG. 1 is a perspective view of a mold for forming a curved press product according to the related art. As illustrated in FIG. 2, in a curved press product 101 according to the related art, a bending portion is not formed at a widthwise end portion of a blank. Accordingly, the widthwise end portion of the blank has low rigidity, and hence has low resistance against a force of shrinking the blank in a longitudinal direction. Therefore, as illustrated in FIG. 3, the excess material resulting from the curved shape is more likely to cause wrinkles, with the result that a large number of wrinkles 140 occur in flange portions 107. Note that, when upper forming sections 31 of the mold are further lowered under the state illustrated in FIG. 2, layers of wrinkles occur when the flange portions 107 are formed by lower surfaces 31 b of the upper forming sections 31 and upper surfaces 36 a of flange-portion forming sections 36 of the mold.

SUMMARY OF THE INVENTION

According to an exemplary embodiment of this disclosure, there is provided a press product forming method for press-forming a curved press product, the curved press product being formed into a hat-like cross-section including: an upper surface portion; side wall portions each bending and extending from a widthwise edge of the upper surface portion in a direction crossing the upper surface portion; and flange portions each bending and extending from an edge of each of the side wall portions, the widthwise edge of the upper surface portion being shaped so as to curve and extend along a longitudinal direction. In some embodiments, the press product forming method includes: a pre-forming step of forming, at a widthwise end portion of a flat plate-like blank, a highly rigid portion extending along the longitudinal direction; and a main forming step of forming the upper surface portion and the side wall portions under a state in which the highly rigid portion is left.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a perspective view of a mold for forming a curved press product according to the related art;

FIG. 2 is a cross-sectional view taken along the line A-A of FIG. 1, for illustrating a forming state in the midst of a main forming step according to the related art;

FIG. 3 is a perspective view of the curved press product in the midst of the main forming step according to the related art;

FIG. 4A is a perspective view of a curved press product according to a first embodiment of this disclosure;

FIG. 4B is a cross-sectional view of the curved press product taken along the line B-B of FIG. 4A;

FIG. 5A is a perspective view of a blank according to the first embodiment of this disclosure after completion of a pre-forming step;

FIG. 5B is a cross-sectional view of the blank taken along the line C-C of FIG. 5A;

FIG. 6 is a perspective view of a mold for forming a curved press product according to an example of this disclosure;

FIG. 7 is a cross-sectional view taken along the line D-D of FIG. 6, for illustrating a forming state in the midst of a main forming step according to the example of this disclosure;

FIG. 8 is a perspective view of the curved press product according to the example of this disclosure in the midst of the main forming step;

FIG. 9 is a cross-sectional view taken along the line D-D of FIG. 6, for illustrating a state after completion of a flange-portion flattening step;

FIG. 10A is a perspective view of a curved press product according to a second embodiment of this disclosure;

FIG. 10B is a cross-sectional view of the curved press product taken along the line E-E of FIG. 10A;

FIG. 11A is a perspective view of a blank according to the second embodiment of this disclosure after completion of the pre-forming step;

FIG. 11B is a cross-sectional view of the blank taken along the line F-F of FIG. 11A;

FIG. 12A is a perspective view of a curved press product according to a third embodiment of this disclosure;

FIG. 12B is a cross-sectional view of the curved press product taken along the line G-G of FIG. 12A;

FIG. 13A is a perspective view of a blank according to the third embodiment of this disclosure after completion of the pre-forming step;

FIG. 13B is a cross-sectional view of the blank taken along the line H-H of FIG. 13A;

FIG. 14A is a perspective view of a curved press product according to a fourth embodiment of this disclosure;

FIG. 14B is a cross-sectional view of the curved press product taken along the line I-I of FIG. 14A;

FIG. 15A is a perspective view of a blank according to the fourth embodiment of this disclosure after completion of the pre-forming step;

FIG. 15B is a cross-sectional view of the blank taken along the line J-J of FIG. 15A;

FIG. 16A is a perspective view of a blank according to another embodiment of this disclosure;

FIG. 16B is a cross-sectional view of the blank taken along the line K-K of FIG. 16A;

FIG. 17A is a perspective view of a blank according to the another embodiment of this disclosure after completion of the pre-forming step;

FIG. 17B is a cross-sectional view of the blank taken along the line L-L of FIG. 17A;

FIG. 18A is a perspective view of a curved press product according to the another embodiment of this disclosure after completion of the flange-portion flattening step; and

FIG. 18B is a cross-sectional view of the curved press product taken along the line M-M of FIG. 18A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of this disclosure are described with reference to the drawings. Note that, in each drawing, W represents a width direction, L represents a longitudinal direction, UPR represents an upper side, and LWR represents a lower side. Further, a drawing viewed from the width direction W illustrates a side view, a drawing viewed from the upper side UPR or the lower side LWR illustrates a plan view, and a drawing viewed from the longitudinal direction L illustrates a front view.

First Embodiment

As illustrated in FIGS. 4A and 4B, a curved press product 1 according to a first embodiment of this disclosure is formed into a hat-like cross-section including: an upper surface portion 3 arranged on the upper side of the curved press product so as to extend in the longitudinal direction L; a pair of right and left side wall portions 5 each extending from a widthwise edge 3 a of the upper surface portion 3 obliquely downward (in a direction crossing the upper surface portion 3) ; and flange portions 7 bending and extending respectively from lower ends 5 a (edges) of the side wall portions 5 to both right and left sides.

The widthwise edge 3 a of the upper surface portion 3 is formed into a convex shape that bulges to the upper side UPR along the longitudinal direction L in side view.

A press product forming method according to this embodiment includes a pre-forming step, a main forming step, and a flange-portion flattening step.

As illustrated in FIGS. 5A and 5B, the pre-forming step is carried out in such a manner that a highly rigid portion 9 extending along the longitudinal direction L is formed at each widthwise end portion of a flat plate-like blank (not shown). Specifically, as in a case of a blank 2, the highly rigid portion 9 includes a bending portion 11 which is formed through bending a widthwise end portion of the blank 2 obliquely to the upper side UPR (front surface side). In some cases, the bending portion 11 and a body portion 13 form an angle θ of, for example, approximately 10° to approximately 90°. Further, in some embodiments, the bending portion 11 is formed into a substantially straight shape in order to prevent occurrence of wrinkles at the time of pre-forming. Note that, after the pre-forming step and before the main forming step, the blank 2 may be heated.

The main forming step is carried out in such a manner that the upper surface portion 3 and the side wall portions 5 are formed in the heated blank 2 using a mold which is described in detail later.

The flange-portion flattening step is carried out in such a manner that the bending portion 11 of the highly rigid portion 9 formed in the pre-forming step is pressed and flattened into the flange portion using the above-mentioned mold. As described above, the main forming step and the flange-portion flattening step may be carried out by hot press forming under a state in which the blank 2 is heated.

After the flange-portion flattening step is finished, the blank is quenched. In this manner, the curved press product 1 that is increased in strength is completed as illustrated in FIG. 4A.

EXAMPLE

Next, procedures for forming the curved press product according to the first embodiment using the mold are described in detail.

As illustrated in FIG. 6, a mold 21 includes an upper die 23 and a lower die 25. The upper die 23 includes a mounting plate 27 and an upper forming die 29 provided under the mounting plate 27. The upper forming die 29 is formed into a U-shape in front view, and includes a pair of right and left upper forming sections 31 extending downward, and a coupling section 32 bridging the upper forming sections 31. Further, the lower die 25 includes a mounting plate 33 and a lower forming die 35 provided on the mounting plate 33. The lower forming die 35 is formed into a T-shape in front view, and includes flange-portion forming sections 36 provided on right and left sides thereof, and a lower forming section 37 formed through protruding upward a center portion thereof in a right-left direction. The lower forming section 37 is fitted between the pair of upper forming sections 31. Further, upper surfaces 36 a of the flange-portion forming sections 36 and an upper surface 37 a of the lower forming section 37 are formed so as to exhibit a convex shape that bulges to the upper side UPR in side view. Note that, as shown in FIG. 7, lower surfaces 31 b of the upper forming sections 31 and a lower surface 32 b of the coupling section 32 are curved so as to conform to the upper surfaces 36 a and the upper surface 37 a of the lower forming die 35. As described above, the mold 21 according to this embodiment is formed of a simply-structured mold (forming mold) which is not provided with a wrinkle prevention device (blank holder) or the like.

As illustrated in FIG. 7, in the main forming step, the upper surface portion 3 is formed in the heated blank in such a manner that a widthwise center portion of the blank is brought into contact with the upper surface of the lower forming section 37, and each side wall portion 5 is formed in the heated blank in such a manner that each widthwise side region of the blank is sandwiched between a side surface 37 b of the lower forming section 37 and an inner side surface 31 a of the upper forming section 31. Here, the bending portion 11 is formed at each widthwise end portion of the blank along the longitudinal direction. Accordingly, the widthwise end portion of the blank 2 has high rigidity, and thus has high resistance against a force of shrinking the blank in the longitudinal direction. Therefore, an excess material resulting from a curved shape is less likely to cause wrinkles. As a result, as illustrated in FIG. 8, wrinkles 40 are less likely to occur in the flange portion 7. Note that, when the upper forming sections 31 are further lowered under the state illustrated in FIG. 7, as illustrated in FIG. 9, in the flange-portion flattening step, each bending portion 11 is pressed by the lower surface 31 b of the upper forming section 31 and the upper surface 36 a of the flange-portion forming section 36. In this manner, the flat flange portion 7 has less wrinkles and no layers of wrinkles.

In the following, operations and effects of this embodiment are described.

(1) According to this embodiment, provided is a press product forming method for press-forming the curved press product 1. The curved press product 1 is formed into a hat-like cross-section including: the upper surface portion 3; the side wall portions 5 each bending and extending from the widthwise edge 3 a of the upper surface portion 3 in a direction crossing the upper surface portion 3; and the flange portions 7 each bending and extending from the edge 5 a of each of the side wall portions 5. The widthwise edge 3 a of the upper surface portion 3 is shaped so as to curve and extend along the longitudinal direction L.

Further, the press product forming method includes: the pre-forming step of forming, at the widthwise end portion of the flat plate-like blank, each bending portion 11 (highly rigid portion 9) extending along the longitudinal direction; and the main forming step of forming the upper surface portion 3 and the side wall portions 5 under a state in which each highly rigid portion 9 is left.

As described above, in the press product forming method according to this embodiment, the upper surface portion 3 and the side wall portions 5 are formed under the state in which each bending portion 11 extending along the longitudinal direction is left. Accordingly, each widthwise end portion of the blank 2 is increased in rigidity, and is increased in resistance against the force of shrinking the blank in the longitudinal direction. Therefore, at the time of forming the upper surface portion 3 and the side wall portions 5, even when the excess material resulting from the curved shape causes action of the force of shrinking the blank in the longitudinal direction, it is possible to prevent or minimize the occurrence of forming defects, such as wrinkles and layers of wrinkles, in the flange portions 7.

(2) Each highly rigid portion 9 includes the bending portion 11 formed through bending the widthwise end portion of the blank 2 obliquely to the front surface side, and hence it is possible to increase rigidity of the widthwise end portion of the blank 2.

(3) The press product forming method according to this embodiment further includes the flange-portion flattening step of pressing and flattening the bending portions 11 (highly rigid portions 9) into the flange portions 7 as illustrated in FIG. 9. Accordingly, it is possible to prevent occurrence of wrinkles in the flange portions 7, and to form the flat flange portions 7. In other embodiments, the flange-portion flattening step is not necessary.

(4) The main forming step and the flange-portion flattening step may be carried out by hot press forming. This further increases the significance of forming the bending portion 11 at each widthwise end portion of the blank 2 so as to increase rigidity of the widthwise end portion. That is, in a case of cold press forming, the blank itself has higher rigidity than in a case of hot press forming. Accordingly, in the case of application of the force of shrinking the blank in the longitudinal direction, or at the time of forming the flange portions, wrinkles and layers of wrinkles are less likely to occur in the flange portions 7. On the other hand, in the case of hot press forming, the blank itself has lower rigidity than in the case of cold press forming. Accordingly, in the case of application of the force of shrinking the blank in the longitudinal direction, or at the time of forming the flange portions, wrinkles and layers of wrinkles are more likely to occur in the flange portions 7. Therefore, the bending portion 11 is formed at the widthwise end portion of the blank 2 to thereby increase rigidity of the widthwise end portion. In this manner, it is possible to effectively prevent occurrence of wrinkles and layers of wrinkles.

Second Embodiment

Next, a second embodiment of this disclosure is described. The same components as those of the first embodiment are denoted by the same reference symbols, and description thereof is omitted.

In the curved press product 1 according to the first embodiment, the widthwise edge 3 a of the upper surface portion 3 is formed into a convex shape that bulges to the upper side UPR along the longitudinal direction L in side view.

However, as illustrated in FIG. 10A, in a curved press product 51 according to the second embodiment, an inner curved widthwise edge 53 a and an outer curved widthwise edge 53 b of an upper surface portion 53 are each formed into an arc shape that curves along the longitudinal direction L in plan view. Note that a cross-sectional shape illustrated in FIG. 10B is the same as that of the first embodiment illustrated in FIG. 4B, and the curved press product 51 is formed into a hat-like cross-section including the upper surface portion 53, side wall portions 55, and flange portions 57. Further, of the flange portions 57, an inner curved flange portion is denoted by 57 a, and an outer curved flange portion is denoted by 57 b.

Similarly to the first embodiment, a press product forming method according to this embodiment includes a pre-forming step, a main forming step, and a flange-portion flattening step.

As illustrated in FIGS. 11A and 11B, the pre-forming step is carried out in such a manner that a highly rigid portion 9A extending along the longitudinal direction is formed at one of widthwise end portions of a flat plate-like blank (not shown). Specifically, as in a case of a blank 52, the highly rigid portion 9A includes a bending portion 58 which is formed through bending a left widthwise end portion of the blank 52 obliquely to the upper side (front surface side). In some cases, the bending portion 58 and a body portion 59 form an angle θ of, for example, approximately 10° to approximately 90°. Further, the bending portion 58 is provided in an outer curved region of the curved press product 51 in plan view. Still further, the bending portion 58 may be formed into a straight shape in order to prevent occurrence of wrinkles at the time of the pre-forming step.

The main forming step and the flange-portion flattening step are the same as those of the first embodiment. Note that, similarly to the above-mentioned first embodiment, the main forming step and the flange-portion flattening step may be carried out by hot press forming under a state in which the blank is heated.

Operations and Effects of this Embodiment are the same as those of the First Embodiment

In particular, rigidity of the widthwise end portion is increased in such a manner that the bending portion 58 is formed at the widthwise end portion corresponding to the outer curved flange portion 57 b in which wrinkles are more likely to occur. Thus, it is possible to effectively prevent occurrence of wrinkles and layers of wrinkles in the outer curved flange portion 57 b.

Third Embodiment

Next, a third embodiment of this disclosure is described. The same components as those of the first and second embodiments are denoted by the same reference symbols, and description thereof is omitted.

As illustrated in FIGS. 12A and 12B, a curved press product 61 according to the third embodiment has the same shape as that of the curved press product 1 according to the first embodiment. That is, the curved press product 61 is formed into a hat-like cross-section including an upper surface portion 3, side wall portions 5, and flange portions 7. Further, a widthwise edge 3 a of the upper surface portion 3 is formed into a convex shape that bulges to the upper side UPR along the longitudinal direction L in side view.

Similarly to the first and second embodiments, a press product forming method according to this embodiment includes a pre-forming step, a main forming step, and a flange-portion flattening step.

As illustrated in FIGS. 13A and 13B, the pre-forming step is carried out in such a manner that triangular ridges 63 (ridges) functioning as highly rigid portions 9B and extending along the longitudinal direction are formed respectively at both widthwise end portions of a flat plate-like blank (not shown). Specifically, as in a case of a blank 62, both the widthwise end portions of the flat plate-like blank are protruded to the upper side (front surface side), to thereby form the ridges 63 each having a dogleg cross-section protruding upward. Further, in some cases, each of the ridges 63 is formed into a straight shape in order to prevent occurrence of wrinkles at the time of the pre-forming step.

The main forming step and the flange-portion flattening step are the same as those of the first and second embodiments. Note that, similarly to the above-mentioned first and second embodiments, the main forming step and the flange-portion flattening step may be carried out by hot press forming under a state in which the blank is heated.

Operations and Effects of this Embodiment are the same as those of the First and Second Embodiments

In particular, the triangular ridges 63 are formed respectively at the widthwise end portions of the blank 62, and thus rigidity of the widthwise end portions is increased. Accordingly, the highly rigid portions 9B can effectively prevent occurrence of wrinkles and layers of wrinkles in the flange portions 7.

Fourth Embodiment

Next, a fourth embodiment of this disclosure is described. The same components as those of the first to third embodiments are denoted by the same reference symbols, and description thereof is omitted.

A curved press product 71 according to the fourth embodiment has the same shape as that of the curved press product 51 according to the second embodiment. That is, as illustrated in FIGS. 14A and 14B, the curved press product 71 is formed into a hat-like cross-section including an upper surface portion 53, side wall portions 55, and flange portions 57. Further, of the flange portions 57, an inner curved flange portion is denoted by 57 a, and an outer curved flange portion is denoted by 57 b. An inner curved widthwise edge 53 a and an outer curved widthwise edge 53 b of the upper surface portion 53 are each formed into an arc shape that curves along the longitudinal direction L in plan view.

Similarly to the first to third embodiments, a press product forming method according to this embodiment includes a pre-forming step, a main forming step, and a flange-portion flattening step.

As illustrated in FIGS. 15A and 15B, the pre-forming step is carried out in such a manner that a triangular ridge 73 (ridge) functioning as a highly rigid portion 9C and extending along the longitudinal direction L is formed at one of widthwise end portions of a flat plate-like blank (not shown). Specifically, as in a case of a blank 72, one of the widthwise end portions of the flat plate-like blank is protruded to the upper side (front surface side), to thereby form the ridge 73 having a dogleg cross-section protruding to the upper side UPR. Further, the triangular ridge 73 is provided in an outer curved region of the curved press product 71 in plan view. Still further, in some cases, the ridge 73 is formed into a straight shape in order to prevent occurrence of wrinkles at the time of the pre-forming step.

The main forming step and the flange-portion flattening step are the same as those of the first to third embodiments. Note that, similarly to the above-mentioned first to third embodiments, the main forming step and the flange-portion flattening step may be carried out by hot press forming under a state in which the blank is heated.

Operations and Effects of this Embodiment are the same as those of the First to Third Embodiments

In particular, the triangular ridge 73 is formed at the widthwise end portion of the blank 72, and thus rigidity of the widthwise end portion is increased. Accordingly, the highly rigid portion 9C can effectively prevent occurrence of wrinkles and layers of wrinkles in the outer curved flange portion 57 b.

Other Embodiment

Next, forming steps according to another embodiment of this disclosure are described step by step. Here, a case of forming a center pillar is described by way of example.

First, a flat plate-like blank 90 is formed of a flat steel plate extending in an elongated manner as illustrated in FIGS. 16A and 16B, and includes a longitudinal center portion 93 having a relatively large width.

Next, in a pre-forming step, a bending portion 95 (highly rigid portion 9D shown in FIG. 17A) is formed in such a manner that each widthwise end portion of the longitudinal center portion 93 of the flat plate-like blank 90 is bent obliquely to the upper side (front surface side). Thus, the blank 90 is formed into a blank 91 illustrated in FIGS. 17A and 17B.

Then, as illustrated in FIGS. 18A and 18B, after an upper surface portion 96 and side wall portions 97 are formed in the heated blank 91 in a main forming step under a state in which the bending portions 95 are left, the bending portions 95 are pressed and flattened into flange portions 98 in a flange-portion flattening step. The blank 91 is then quenched so as to be increased in strength. Thus, a center pillar 99 according to this embodiment is completed. Note that, similarly to the above-mentioned first to fourth embodiments, the main forming step and the flange-portion flattening step may be carried out by hot press forming under a state in which the blank is heated.

As described above, according to this embodiment, even in a case where the highly rigid portions 9D are formed in a part of the longitudinal portion of the blank 91, it is possible to effectively prevent occurrence of wrinkles and layers of wrinkles in the flange portions 98.

The first to fourth embodiments and another embodiment of this disclosure are described above, but this disclosure is not limited thereto. Various modifications and changes can be made thereto.

For example, in the first to fourth embodiments and another embodiment, the bending portion is extended obliquely to the upper side (front surface side), but may be extended to the lower side (back surface side).

Further, regarding the ridge, a shape other than the triangular ridge is also applicable. However, in order to prevent a layered portion from being formed in a ridge when pressing the ridge in the flange-portion flattening step, a ridge having a ridge line, such as the triangular ridge, is preferred.

In addition, in the above-mentioned embodiments, the highly rigid portions 9 to 9C are pressed and flattened, but the highly rigid portions 9 to 9C may be left unpressed and unflattened in the obtained products.

Further, the press forming according to this disclosure may include cold press forming which does not require heating of a blank and quenching performed after forming. 

What is claimed is:
 1. A press product forming method for press-forming a curved press product, the curved press product being formed into a hat-like cross-section including: an upper surface portion; side wall portions each bending and extending from a widthwise edge of the upper surface portion in a direction crossing the upper surface portion; and flange portions each bending and extending from an edge of each of the side wall portions, the widthwise edge of the upper surface portion being shaped so as to curve and extend along a longitudinal direction, the press product forming method comprising: a pre-forming step of forming, at a widthwise end portion of a flat plate-like blank, a highly rigid portion extending along the longitudinal direction; and a main forming step of forming the upper surface portion and the side wall portions under a state in which the highly rigid portion is left.
 2. A press product forming method according to claim 1, wherein the main forming step is carried out by hot press forming.
 3. A press product forming method according to claim 1, further comprising a flange-portion flattening step of pressing and flattening the highly rigid portion into one of the flange portions.
 4. A press product forming method according to claim 3, wherein the main forming step is carried out by hot press forming.
 5. A press product forming method according to claim 1, wherein the highly rigid portion comprises at least one of: a ridge which protrudes to at least one of a front surface side and a back surface side of the flat plate-like blank; and a bending portion which is formed through bending the widthwise end portion of the flat plate-like blank obliquely to at least one of the front surface side and the back surface side of the flat plate-like blank.
 6. A press product forming method according to claim 5, wherein the main forming step is carried out by hot press forming.
 7. A press product forming method according to claim 5, further comprising a flange-portion flattening step of pressing and flattening the highly rigid portion into one of the flange portions.
 8. A press product forming method according to claim 7, wherein the main forming step is carried out by hot press forming.
 9. A press product forming method comprising: providing a substantially flat plate-like blank; pre-forming the blank to create at least one bending portion at or near a widthwise end portion of the blank, the at least one bending portion extending along a longitudinal direction of the blank; forming the pre-formed blank into a curved press comprising a hat-like cross-section including: an upper surface portion; side wall portions each bending and extending from a widthwise edge of the upper surface portion at an angle from the upper surface portion; and flange portions each bending and extending from an edge of each of the side wall portions, the widthwise edge of the upper surface portion curving and extending along the longitudinal direction, wherein the step of forming the pre-formed blank into the curved press is such that the upper surface portion and the side wall portions are formed while the at least one bending portion remains intact.
 10. The method of claim 9, wherein the step of forming the pre-formed blank into the curved press comprises hot press forming.
 11. The method of claim 9, further comprising pressing and flattening the at least one bending portion into one of the flange portions.
 12. The method of claim 11, wherein the step of forming the pre-formed blank into the curved press comprises hot press forming.
 13. The method of claim 9, wherein the at least one bending portion comprises at least one of: a ridge which protrudes from at least one of a front surface side and a back surface side of the flat plate-like blank; and a bent flange formed by bending the widthwise end portion of the flat plate-like blank obliquely relative to at least one of the front surface side and the back surface side of the flat plate-like blank.
 14. The method of claim 13, wherein the step of forming the pre-formed blank into the curved press comprises hot press forming.
 15. The method of claim 13, further comprising pressing and flattening the at least one bending portion into one of the flange portions.
 16. The method of claim 13, wherein the ridge is triangular in cross-section.
 17. The method of claim 9, wherein the step of pre-forming the blank comprises creating at least two bending portions, with a first bending portion extending along the longitudinal direction of the blank at a first widthwise end portion of the blank and the a second bending portion extending along the longitudinal direction of the blank at a second widthwise end portion of the blank.
 18. The method of claim 13, wherein the bent flange extends from the at least one of the front surface side and the back surface side at an angle between approximately 10° and approximately 90°. 